Sigmoidoscopy Could Thwart a Third of Colorectal Cancers

Participants were randomly allocated to the intervention group (offered flexible sigmoidoscopy screening) or the control group (not contacted). The primary outcome measures were the incidence of colorectal cancer, including prevalent cases detected at screening, and mortality from colorectal cancer. In all, 113,195 people were assigned to the control group and 57,237 to the intervention group, of whom 71% underwent sigmoidoscopy.

The results showed that during screening and a median follow-up of 11.2 years, 2,524 participants were diagnosed with colorectal cancer (1,818 in control group and 706 in the intervention group) and 20,543 died, 727 of them from colorectal cancer (538 versus 189, respectively). In intention-to-treat analyses, colorectal cancer incidence in the intervention group was reduced by 23% and mortality by 31%. In per-protocol analyses--adjusting for self-selection bias in the intervention group--incidence of colorectal cancer in people attending screening was reduced by 33%, and mortality by 43%; incidence of distal colorectal cancer (rectum and sigmoid colon) was reduced by 50%. The researchers suggest that according to the results, flexible sigmoidoscopy will save one life for every 400 people who undergo the test; but they add that as follow-ups continue and the screened population ages, these results are expected to improve. The study was published online on April 28, 2010, in the Lancet.

"This is an extraordinarily large proportion,” said coauthor Jane Wardle, Ph.D., from the department of public health at University College. "Despite pessimistic predictions that healthy people would be unwilling to undergo an unpleasant procedure, there was a good uptake, with slightly more men than women, and people told us that they are happier and were reassured about their future health.”

Colorectal cancer is the third most common cancer worldwide and has a high mortality rate. Colorectal cancers arise from adenomatous polyps in the colon, mushroom-shaped growths that are usually benign, but may develop into cancer over time. Diagnosis is commonly made via sigmoidoscopy, in which a lighted scope is inserted into the rectum and lower colon to check for polyps and other abnormalities. A more invasive option is colonoscopy, in which the entire colon is examined for polyps and other abnormalities that may be caused by cancer. A colonoscopy has the advantage that if polyps are discovered during the procedure, they can be immediately removed and the tissue taken for biopsy.

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